1) Field of the Invention
The present invention relates to a variable spectroscopic element.
2) Description of Related Art
There has been known a variable spectroscopic element provided with an etalon device and a control section (See JP KOKAI No. 2008-1291, for example), in which a pair of optical substrates are arranged to face each other with a spacing between and at least one of the optical substrates is made movable by use of actuators such as piezoelectric elements, so that the optical property is changeable by change of intersurface distance between the optical substrates or between reflecting films formed on the optical substrates (hereafter, generally referred to as “intersurface distance between optical substrates”).
Of such a variable spectroscopic element, there has been known a type (for example, JP KOKAI No. Hei 6-241899) in which, for the purpose of setting the intersurface distance between optical substrates to have a desired value, capacitive sensors for measuring the intersurface distance are arranged on the mutually facing surfaces to measure the instant intersurface distance at a predetermined sampling interval, comparison is made between the intersurface distance as measured and a desired intersurface distance, and the intersurface distance is adjusted by actuating actuators based on the comparison result.